Angle Conversion
Angles In Circles Tutorial for calculating angles in circles formed from radii, chords, tangents and secants.

Calculator for Constructing Regular Polygons

Draw a circle, measure the radius and this calculates the length of the polygon's sides.

Central Angle Calculator Calculates a Circle's Central Angle, Radius or Arc Length

Circle Circumference & Area Calculator

CIRCLE Calculator for Radius, Central Angle, Chord, Segment Height, Apothem, Arc Length and Chord Length. If you know two, it will calculate the other five as well as the Sector Area, Segment Area and Circle Area.

Circle Equation Tutorial

Explains equations of the type x² + y² = r²

Circle Equation Calculator

Input 3 points and it calculates a circle's center radius and equation.

Ellipses
Calculator and tutorial

Types of Triangles
A chart showing triangles classified by angles
(acute, right, obtuse) and by sides (equilateral, isosceles, scalene).

Also has triangle area formulas and a triangle area calculator.

Triangle Centers
A tutorial discussing the incenter, circumcenter, centroid, orthocenter and the Euler line.

Triangle Tester
Calculates if 3 sides will form a triangle or not.

Right Triangles (Pythagorean Theorem)

30 60 90 and 45 45 90 Triangle Calculator

Regular Polygon Calculator
Input the number of sides and the side length and it calculates the polygon perimeter, all angles (interior, central and exterior), the inradius, the circumradius and the total area.

Rhombus Calculator
Input side length and either angle and it calculates the area, both diagonals, altitude, perimeter.

Input both diagonals and it calculates the side, area, altitude, perimeter and both angles.

Quadrilateral page Descriptions and graphics discussing 6 different types of quadrilaterals.

Trapezoid Calculator

How to Calculate Trapezoid Area

Calculator for Parallelograms Squares Rectangles Rhombuses

Quadrilateral Kite Calculator